Conventional machine dishwashing detergents generally contain an available chlorine releasing agent and a polyphosphate builder as critical components. The chlorine agent, such as 2-3% sodium dichloroisocyanurate, has generally been found to be necessary to achieve spot free glassware. The polyphosphate, typically sodium tripolyphosphate, seemed vitally important to provide adequate soil removal, inhibit soil redeposition and prevent hard water salt deposits on glassware and other utensils.
The necessity of incorporating an available chlorine releasing agent in a detergent has many drawbacks. One obvious one is the objectionable chlorine like odor released during the hot washing operation. Another is the significant additional cost of the formulation as the desirable available chlorine releasing agents are relatively expensive. A more important drawback is the inherent instability of available chlorine releasing agents when formulated into detergent compositions. The detergent will continually lose available chlorine during storage, resulting in limited shelf-stability. Therefore, it is common practice to add extra chlorine agent at the time of manufacture to compensate for loss during storage. This adds to the cost of the product and merely extends the shelf-life which is still limited.
A major, and in the case of liquid detergent compositions, the most serious limitation of having a chlorine agent in the formulation is the incompatibility of these strong oxidizing agents with organic additives, particularly low-foaming surfactants. The presence of a low-foaming surfactant is desirable because it can add significantly to the performance of the detergent by providing increased cleaning action and preventing soil redeposition. Even more importantly, when soil loads are high, some low-foam surfactants will defoam the protein food soil stabilized foam which markedly reduces the mechanical efficiency of the wash spray. The reactions of oxidizing chlorine agent and the surfactant will be evidenced by an increased rate of loss of available chlorine and a gradual loss of surfactant performance, particularly in food soil defoaming capability.
In granular or powdered formulations, the incompatibility results in short shelf-life. In the liquid or slurry type of formulations, the reaction of chlorine agent and low-foam surfactant in solution is rapid enough to prevent any attempt to incorporate low-foaming surfactants into the formulation. Therefore, the performance of liquid (or gel) machine dishwashing detergents is noticeably inferior to granular or powder low-foam surfactant containing dishwasher detergents.
Prior attempts to avoid the problems associated with including available chlorine releasing agents have been primarily in the direction of using milder oxidizing agents, such as the "oxygen bleaches"; peroxides, perborates and persulfates. However, these agents do not produce the spot free glassware achieved when the chlorine bleaches are used.
None of the prior art teaches the elimination of chlorine agents by the use of hydrophobe/maleic acid copolymers in machine dishwashing detergent compositions.
The desirability of avoiding phosphates in detergents is well recognized. Phosphorus based compounds when present in lakes, rivers, and bays, serve as nutrients for algae growth, resulting in the deterioration of water quality. Environmentally acceptable detergents are those free of polyphosphates and other sources of phosphorus. Even though polyphosphates have been reduced or eliminated from household laundry detergents in many countries, machine dishwashing detergents have always been exempted from the phosphate ban on the basis of studies by machine dishwashing detergent manufactures. These studies indicate polyphosphates are necessary for acceptable washing performance.
Development of machine dishwashing detergents using substitutes for phosphate containing compounds has been addressed in the patent literature. U.S. Pat. No. 4,203,858 teaches using a low molecular weight polyacrylic acid in a phosphate free machine dishwashing composition. U.S. Pat. No. 4,608,188 teaches the use of a maleic acid/acrylic acid copolymer. Our testing demonstrates these polymers do not give the superior performance of the hydrophobe containing maleic acid copolymer of the present invention.
U.S. Pat. No. 3,764,559 teaches the use of detergent compositions containing maleic anhydride polymers as a means to eliminate phosphates. The polymers used in this patent are maleic anhydride copolymerized with vinyl acetate, utilized at a broad level of 5% to 65%, and a more preferred range of 20% to 50% by weight of the copolymer.
U.S. Pat. No. 4,102,799 teaches the use of detergents essentially free of inorganic phosphates. The detergents were shown to have improved effects on overglaze through the use of citrate substitution. However, these detergents also contains organic phosphorus compounds in the form of phosphonates, so the compositions are not truly phosphorus free. In addition, the detergent compositions of U.S. Pat. No. 4,102,799 contain from about 0.5 to 5 percent by weight of a bleaching agent.
U.S. Pat. No. 4,182,684 teaches phosphate free machine dishwashing detergent compositions by using from 5 to 90 percent by weight of a polymeric compound. The detergent composition disclosed in U.S. Pat. No. 4,182,684 also contains a chlorine containing compound, providing from 0.5 to 2 percent by weight available chlorine.
Other patents which include polymeric materials are European Patent 132,792, German Patent DE 3627773-A, and UK Patent Application GB 2,203,163-A. EP 132,792 teaches certain cleaning compositions for washing dishes in automatic dishwashers. The compositions contain from 1 to 8 weight percent of a polycarboxylic acid having molecular weight of 12,000 to 40,000. In addition, the detergent contains alkaline surfactants and standard additives such as bleaching agents, biocides, perfumes, foaming-inhibitors, and/or solubilizers. The polymer can be polyacrylic or polymethacrylic acid or polymers of maleic acid or fumaric acid and ethylene or propylene.
German Patent DE 3627773-A teaches a phosphate free detergent composition utilizing a crystalline alkali layered silicate with a polymeric material. The composition also makes use of a defoaming surfactant and an available chlorine source.
GB 2203163-A teaches the use of a polyacrylic acid and a polyhydroxy acrylic acid in a liquid dishwashing composition. However, this dishwashing detergent composition also requires the use of 3-15% by weight sodium hypochlorite and 0.4 to 6 percent by weight of a chlorine-resistant phosphonate or organic phosphate.
Some patents also exist for phosphate-free detergent compositions which are liquids or pastes, such as Canadian Patent 1,158,522, UK Patent Application GB 2,210,055 and Canadian Patent 1,058,040. Canadian Patent 1,158,522 describes phosphate-free liquid dishwashing compositions containing a partially neutralized aminocarboxylic acid, a water soluble salt of a nitrogen-free linear polymer containing carboxyl groups and a low-foaming nonionic surfactant. Canadian Patent 1,158,522 utilizes environmentally unacceptable nitrogen containing aminocarboxylic salts, such as nitrilotriacetic acid or ethylene diamine tetraacetic acid.
GB 2,210,055 describes the use of polymer (polyacrylate) with zeolite to achieve performance. This composition also contains a chlorine source. Since the normal stabilizers are not chlorine stable, the composition of the GB 2,210,055 Application tends to stratify on standing. Canadian Patent 1,058,040 also teaches the use of water insoluble zeolites for the builder. When used as dishwashing detergents, because the zeolite is insoluble, deposits form on the glasses in the course of the cleaning operation.
Several other patents make use of polymeric additives in dishwashing detergent compositions, but they also teach the use of phosphates and chlorine. These patents are DE 2,304,404-A, EP 271,992-A, and UK Patent Application GB 2,163,447-A.
Because of the effective performance of the chlorine free detergent composition of this invention, chlorine sensitive materials can now be added to the detergent composition.